Nutrition of the Weaned Holstein Calf. II. Effect of Dietary Protein Level on Nitrogen Balance, Digestibility and Feed Intake

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Abstract
Four cracked corn-based diets supplemented with 0, 5, 10 and 15% soybean meal (SBM) were fed to weaned male Holstein calves to study effects of protein level on digestibility and nitrogen balance, in one trial, and on feed intake, in another. Twleve calves were used in each trial in a replicated 4 × 4 Latin square design. Calves were 9 to 12 weeks of age at the start of the experiment and diets ranged from 9.9 to 16.2% crude protein (CP). In trial T, feed intake was restricted to 80 g dry matter (DM) per kilogram metabolic body weight (W.75). There was a linear change (P<.01) in apparent DM digestibility, increasing from 71.1% with the low protein diet to 75.1% with the high protein diet. Similar significant trends were observed in digestibility of organic matter (71.2 to 75.3%), nitrogen (61.6 to 72.2%), acid detergent fiber (36.2 to 44.8%) and starch (86.3 to 89.7%). Fecal starch decreased, from 28.4 to 22.1% of DM, and fecal pH increased, from 5.21 to 5.52, as SBM was substitued for corn; both of these trends were significant (P<.01, linear component); they were also correlated (r = −.55, P<.01). Nitrogen (N) retention increased with dietary protein level (P<.01, linear component), from 9.0 to 10.9 to 11.9 to 13.2 g N/kg digestible organic matter intake for diets 1 through 4, respectively. The same percentage of nitrogen intake was retained on all diets, but the amount of absorbed nitrogen that was retained decreased with dietary protein level (P<.01, linear component) from 63.0% with 9.9% CP to 51.4% with 16.2% CP. In trial 2, voluntary feed intake averaged 98.2, 110.1, 106.3 and 106.5 g DM/W.75 for diets 1 to 4, respectively, (P<.05, quadratic component). Live weight gain increased in a linear manner (P<.01) with increasing CP, from .77kg/day with diet 1 to 1.22 kg/day with diet 4. Copyright © 1980. American Society of Animal Science . Copyright 1980 by American Society of Animal Science.